The present invention concerns a needle cap device for a pre-fillable one-time injection apparatus with an injector needle firmly connected to an injector head and the resulting improved injection apparatus. This needle cap comprises a stiff plastic outer casing made of a hard elastic material, which is provided with an interior sealing lining member made of a soft elastic material. This needle cap is easily put on the injector head and without any preparatory steps is completely removable from it. The injector head and the stiff plastic outer casing have elements of a mechanically stable form and/or elements providing a force-locking connecting device around the insertion path for the cap, with a microbiologically secure seal when the stiff plastic outer casing is on the injector head.
A pre-filled, one-time injection apparatus, also called a syringe, should be made from glass or plastic, and must be provided during storage with a needle cap, which is removed immediately prior to use, for protection of the injector needle and contents to be injected. The injector needle is also designated a hollow injection needle and the needle cap is designated a protective cap.
This type of needle cap is known and on the market in many different embodiments. Needle caps, which are made from elastomer, preferably synthetic rubber or natural rubber, so-to-say the classical needle cap, are most widely distributed or used. The length of the cap is typically selected so that the tip of the injector needle is inserted in the cap tip when the cap is put on the injector head and remains enclosed and sealed by the material of the cap.
A needle cap of this kind combined with the injector needle firmly connected to the injector head, for example, is known and described by DE-27 17 830 A1 (there by FIG. 6) and DE-44 38 360 A1. Also DE 4 234 319 A1 discloses a needle cap with an elastic cap shroud, which conforms to the injector head. The needle cap of this kind has, on the one hand, the advantageous property that it is easily put on and removed from the injector head without preliminary preparation steps, and also a reliable microbiological seal is guaranteed since the elastic cap shroud conforms to the injector head. However this arrangement has the following disadvantageous properties:
The needle cap can oppose mechanical influences only to a limited extent because of the softness of the material. It can also be penetrated by the needle so that it poses a not insignificant danger of injury to the user.
The needle cap is pressed together when it is removed and contacts on the hollow needle surface. This leads, at least partially, to stripping off of silicone on the needle which serves as a sliding agent for the injection process. If this sliding agent is removed, the injection is associated with pain caused by the injection process. Silicone particles/droplets are thus formed which can enter the body in which the injector needle is inserted.
The assembly of the needle cap is difficult since a reliable controllable displacement limit is absent for the process of placing the needle cap over the injector needle so that the needle cap can easily be pushed too far or too little on the injector head over the needle. Both cases are very disadvantageous since in the first case the needle can poke through the needle cap and in the second case a reliable microbiological seal is no longer guaranteed.
The injector needle is not controllable and/or observable visually by the user with the needle cap placed over the needle on the injector head, to determine, for example, whether the needle is suited for the predetermined purpose or the needle is bent, contaminated or damaged. The needle cap must be removed and if necessary again placed on the injector body with the accompanying great danger of microbiological contamination of the needle, or even of the contents of the needle, and/or of penetration of the needle cap or of needle bending.
During removal of the needle cap a low pressure is produced in the needle tip so that liquid filled in the injector device easily issues from it. It is necessary for the user to remove this liquid drop, which reduces for one thing the actual applied dosage and, for another, the outer needle surface is wetted with medicine. During the injection an indefinite amount of medication is brought into the duct in the needle which is generally undesirable and can lead to bleeding at the insertion location with a few medicines, e.g. anticoagulants (Heparin etc.).
For improvement of the mechanical properties of this type of needle cap it is known to provide the needle cap with an outer hard elastic shell as described in EP 0 429 052. Although needle caps of this type are better protected against mechanical influences and also against penetration by the needle, thus avoiding the above-mentioned injury danger, the other disadvantages--no visual control and no observability of the needle when the needle cap is on the injector head, no drop-free removal of the needle cap, stripping of the needle siliconization and no reliable displacement limit for the cap during assembly.
An additional disadvantage in this embodiment is the limited ability to sterilize the needle with the needle cap covering it: a sterilization with a high energy light flash is not possible, similarly the hard outer jacket prevents a sterilization with steam due to insufficient penetrability of steam through this two-part needle cap.
The alternative needle cap described in the above-mentioned DE 44 38 360 A1 has similar disadvantages. This needle cap includes a plastic outer casing of comparatively hard elastic material which is lined inside with a soft elastic sealing material, at least in the vicinity of the hollow needle point. Because of that this soft elastic material can be selected for optimum sealing properties (sealing function), while the hard elastic material is suitable to counter exterior mechanical damage (protective function).
This known needle cap does not fulfill the following criteria: a) reliable sealing of the tip of the needle, b) visual inspection of the needle with the needle cap placed over it, c) reliable drop-free removal of the needle cap, d) no damage to the siliconization on the needle, e) complete removability of the injector head without preparatory steps, f) sterilizability by light flash, steam sterilization, g) reliable connection of the cap to the injector by definite and controllable positioning and g) reliable resealing of the injector after use.
A needle cap was disclosed with the above-mentioned features in German Utility Model Nr. 89 06 101 which does guarantee a reliable sealing and application of the needle tip. The above-described criteria are however also not fulfilled with this known needle cap.